An oil or gas well relies on inflow of petroleum products. When drilling an oil or gas well, an operator may decide to leave productive intervals uncased (open hole) to expose porosity and permit unrestricted wellbore inflow of petroleum products. Alternately, the hole may be cased with a liner, which is then perforated to permit inflow through the openings created by perforating.
When natural inflow from the well is not economical, the well may require wellbore treatment termed stimulation. This is accomplished by pumping stimulation fluids such as fracturing fluids, acid, cleaning chemicals and/or proppant laden fluids to improve wellbore inflow.
In one previous method, the well is isolated in segments and each segment is individually treated so that concentrated and controlled fluid treatment can be provided along the wellbore. Often, in this method a tubing string is used with inflatable element packers thereabout which provide for segment isolation. The packers, which are inflated with pressure using a bladder, are used to isolate segments of the well and the tubing is used to convey treatment fluids to the isolated segment. Such inflatable packers may be limited with respect to pressure capabilities as well as durability under high pressure conditions. Generally, the packers are run for a wellbore treatment, but must be moved after each treatment if it is desired to isolate other segments of the well for treatment. This process can be expensive and time consuming. Furthermore, it may require stimulation pumping equipment to be at the well site for long periods of time or for multiple visits. This method can be very time consuming and costly.
Other procedures for stimulation treatments use tubing strings without packers such that tubing is used to convey treatment fluids to the wellbore, the fluid being circulated up hole through the annulus between the tubing and the wellbore wall or casing.
The tubing string, which conveys the treatment fluid, can include ports or openings for the fluid to pass therethrough into the borehole. Where more concentrated fluid treatment is desired in one position along the wellbore, a small number of larger ports are used. In another method, where it is desired to distribute treatment fluids over a greater area, a perforated tubing string is used having a plurality of spaced apart perforations through its wall. The perforations can be distributed along the length of the tube or only at selected segments. The open area of each perforation can be pre-selected to control the volume of fluid passing from the tube during use. When fluids are pumped into the liner, a pressure drop is created across the sized ports. The pressure drop causes approximate equal volumes of fluid to exit each port in order to distribute stimulation fluids to desired segments of the well.
In many previous systems, it is necessary to run the tubing string into the bore hole with the ports or perforations already opened. This is especially true where a distributed application of treatment fluid is desired such that a plurality of ports or perforations must be open at the same time for passage therethrough of fluid. This need to run in a tube already including open perforations can hinder the running operation and limit usefulness of the tubing string.
Some sleeve systems have been proposed for flow control through tubing ports. However, the ports are generally closely positioned such that they can all be covered by the sleeve.